Undervoltage tripping device for circuit breakers



Sept. 15,1959 H. L..PEQEK 2,904,730

UNDERVOLTAGE TRIPPING DEVICE FOR CIRCUIT BREAKERS Filed July 3, 1956 2 Sheets-Sheet 1 amm WW I" J me/Ya Sept. 15, 1959 H. L. PEEK 2,904,730

UNDERVOLTAGE TRIPPING DEVICE FOR CIRCUIT BREAKERS Filed July 3, 1956 2 Sheets-Sheet 2 5040/0/0 4/2? GAP HAW/wk Mew l. five Y4 4 4 M 5 MW UNDERVOLTAGE TRIPPING DEVICE FOR CIRCUIT BREAKERS Henry L. Peek, Wellesley, Mass., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application July 3, 1956, Serial No. 595,734

7 Claims. (Cl. 317-199) This invention relates generally to circuit breakers for interrupting an electrical circuit and more particularly to a new and improved undervoltage trip device used in combination therewith.

The undervoltage trip device for circuit breakers provides a means for automatically tripping the breaker when the voltage of the protected power system drops below a predetermined value. The users of large air and other types of power circuit breakers frequently require such solenoid operated undervoltage trip devices to trip between thirty and sixty percent of the voltage rating of its coil and pick up and reset at eighty percent of its voltage rating. In order to provide satisfactory operation of a circuit breaker structure embodying an undervoltage trip device, the voltage difference of the trip devicescoil between the pickup and trip values :pressedspring will break open the air gap of the solenoid and as the air gap widens the spring force remains always below but very near the eighty percent voltage pull curve of the solenoid. The force available to-trip a circuit breaker is the difference betweenthe spring force and the solenoid force at whatever decreased voltage the solenoid has imposed upon it. With this arrangement, the force available to tripis held to a maximum. In fact, sufiicient force is available to trip the circuit breaker once the trip device has dropped out eventhough the voltage impressed upon its coil does not'decrease' below sixty percent into the thirty to sixty percentvoltage range.

It is, therefore, onebhject of the present invention to provide a new and improved circuit breaker structure.

Another object of this invention is: to provide a new and improved undervoltage trip device.

A further object of this invention is to provide a new and improved undervoltage trip device in whicha solenoid-spring combination satisfies all of the requirements of undervoltage circuit breaker tripping.

.A still further object of this invention is to provide a 'new and improved undervoltage trip device which utilizes a spring designed to have a logarithmically shaped forcedeflection curve which is so related to the logarithmically shaped characteristic solenoid pull curve that when the voltage impressed upon the winding of the solenoid de- United States Patent i shaped characteristic 'solenoid 'pull curve that when the Patented Sept. 15, 19 59 ice voltage drops to sixty percent of rated voltage the compressed spring biasing means will break open the air gap of the solenoid and as the air gap widens the spring biasing force remains below but very near the eighty percent voltage pull curve of the solenoid.

A still further object of this invention is to provide a new and improved time delayed undervoltage trip device employing a solenoid-spring combination for undervoltage tripping.

" Objects and advantages other than those set forth will be apparent from the following description when read in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a circuit breaker structure and undervoltage trip device therefor embodying the present invention;

Fig. 2 is an enlarged view of the undervoltage trip device shown in Fig. 1;

Fig. 3 is a diagrammatic view of a modification of the undervoltage trip device shown in Figs. 1 and 2 wherein a conical armature biasing spring is used; and

Fig. 4 is a graph of the force-solenoid air gap charac teristics of the undervoltage trip devices illustrated in Figs. 1 to 3, inclusive.

Referring more particularly to the drawings by characters of reference, Fig. 1 illustrates a circuit breaker 10 for protecting an electric circuit (not shown). Breaker 10 and its component parts are mounted on a panel 11 which supports a pair of conductive studs 12 and 13. Mounted on the extremities of studs 12 and 13 are finger contacts 14 and 15 which connect breaker 16 in series with the power circuit controlled. Stud 12 is co-nductively connected to a contact block 16 and stud 13 is conductively connected to a contact block 20'.

A spring biased current carrying finger contact 18 is fulcrumly mounted on contact block 16 to cooperate with a movable contact arm 19 pivotally mounted on a contact block 20. This current path from stud 12 through contact block 16, finger contact 18, movable contact 19, contact block 20, and stud 13 is designated as the primary current path through the breaker 10. V

A secondary or arcing current path includes an arcing movable contact arm 22 which is pivotally carried by and mounted on contact arm 19 at a pivot 23. An arcing contact tip 24 of suitable material is secured to the end of arm 22 which cooperates with an arcing contact 25 afiixed to one end of an arc runner 26. Arcing runner 26 and arcing contact 25 are afiixed to contact block 16.

When breaker 10 is in a closed position (as shown in Fig. l) arcing contact 24 of arcing contact arm 22 is biased by a spring '27 carried by contact arm 19, against arcing contact 25 carried by contact block 16. Contact arm 19 which is integral at its top part 30 is cut apart at its bottom part 31 to form two legs physically and electrically insulated from each other by an insulating washer 32. The secondary or arcing current path is energized from contact block 16 through arcing contacts 25, 24, contact arm 22, pivot 23, the lower part 31 of contact arm 19, leg 33 of contact arm 19, the upper portion 30 of contact arm 19 and thence through contact arm 19 to contact block 20 thereby aiding the primary current path. This loop shaped secondary current path creates electromagnetic forces of sufiicient magnitude to efiectively oppose the large repelling electromagnetic forces exerted upon contact 24 and contact arm 22 by currents of short circuit magnitude during the period of contact engagement or disengagement.

The undervoltage trip device 35 of breaker 10 is illustrated as being energized through a pair of terminals 36 which are usually connected across a pair of the conductors of the three phase power circuit controlled. Device 35 comprises a magnetizable core 37 with a coil 38 mounted therein and magnetically coupled therewith.

An armature 39 forming a part of relay trip device is mounted within coil 38 for movement longitudinally thereof and is responsive to voltage changes in the power circuit controlled. Armature 39 is connected through a bell crank arm member 40 to a piston member 41 mounted in a housing 42. A pair of axially arranged spring biasing means 43 and 44 are arranged around a piston rod 107 of piston member 41 to preload armature 39 of the undervoltage trip device 35. When a drop in voltage occurs (below a predetermined value) the force exerted on the bell crank by the spring biasing means 43 and 44 overcomes the magnetic attraction on the armature 39, causing the armature to leave the pole head of core 37 and trip the breaker. A time delay device 46 is fastened to bell crank member 48 and acts to control the time in which the pre-loaded spring biasing means 43 and 44 respond to trip the breaker. For those applications in which instantaneous undervoltage trip is required, the time delay device 46 is omitted.

Armature 39 has mounted thereon a tripping hammer 47 which initiates operation of the breaker opening mechanism. This tripping mechanism includes a block 48 which is mounted on a trip shaft 49 journaled in breaker 10. Block 48 is fixed to trip shaft 49 causing the trip shaft to rotate when block 48 is rotated. When shaft 49 is rotated, block 108 secured thereto actuates a roller 51 of the Y-shaped star wheel 50. Y-shaped star wheel 50 is pivotally carried by breaker 10 and supports a roller 51 mounted on one of its legs for engagement with block 198. A trip rocker 53 having first and second rocker arms 54 and 55 is pivotally carried by breaker 18 at a pivot 56. Pivotally mounted on rocker arm 55 is a roller 57 which engages one of the legs of the star wheel 50 in endwise engagement. The end of rocker arm 54 is provided with an outer surface 58 which is eccentrically ground with its geometric center within the rocker 53 but above its pivot 56. Therefore, pressure exerted on the outer surface 58 of rocker arm 54 will produce a clockwise turning torque (as viewed in Fig. l) on the rocker 53 about its pivot 56. A cam plate 59 having an arcuate inner cam opening 60 is mounted on breaker 10 and is adjacent rocker 53. An operating arm 62 is mounted adjacent rocker 53 and is provided at one end thereof with a pin 63 which projects through cam plate 59 at the cam opening 60. Pin 63 has a roller journaled thereon which is free to rotate but is firmly held against axial movement by pin 63 and operating arm 62. The roller on pin 63 abuts and engages the outer surface 58 of rocker arm 54. A trip latch 64 having a cam surface 65 is pivotally carried by the operating arm 62 at its pin 63. The other end of operating arm 62 is mounted on a pivot element 67 for pivotally attaching an insulating arm 68 and an indicating link 69.

Operating arm 62 has a changing pivot point 70 which shifts from the contact closed position shown in Fig. l to a contact open position, not shown. A lever 71 pivotally mounted at 72 to the breaker 10 is secured to pin 63 to fix the operating arm to the breaker structure. A trip pin 73 is mounted on a trip latch bar 74 and engages cam surface 65 of the trip latch 64. Trip latch bar 74 is pivotally mounted on a shaft 76. A spring 77 connected to breaker 10 and arm 62 biases the operating arm 62 and a roller 78 mounted on pivot point 70 into engagement with a cam surface '79 of bar 74. Spring 77 also biases trip latch 64 and particularly its cam surface 65 against pin 73.

A manual reclosing mechanism 82 comprising a handle 83 mounted on a shaft 84 journaled in breaker 10 may be used to close the breaker by hand. A closing cam 85 affixed to shaft 84- and mounted within an opening 86 of a lever arm 87 engages a roller 88 mounted on arm 87 when handle 83 is rotated to circuit closed position. Cam

85 upon rotation thereof pushes roller 88 and lever arm 8'7 upward. upward movement of arm 87 carries cam bar 74 with it. Bar 74 is provided with a pin 89 which extends into a slot 90 in arm 87. Upon rotation of handle 83 and shaft 84, pin 89 engages the lower end of slot 90 and upon further movement of handle 83 rotates bar 74 about its pivot 76.

In the contact open position roller 7 8 rests in a curved surface of the cam surface 79 of bar 74. Upon rotation of handle 83 to contact closed position the cam actuates arm 87 upward and arm 87 through the medium of pin 89 of bar 74 and slot of arm 87 rotates bar 74 counterclockwise causing cam surface 79 to slide on roller 78 until the position illustrated in Fig. l is reached.

Insulating arm 68, which is pivotally attached at one end to operating arm 62, is also pivotally attached at its opposite extremity to contact arm 19 at pivot 92. Indicator link 69 is pivoted at pivot 93 and is pivotally connected at one end to a link 94 and at the other end to arm 68 at pivot 67. Link 94 is supported by a shaft 95 which supports an open-closed breaker indicator 97.

The opening of breaker 10 (shown in Fig. 1 in a closed position) occurs when an undervoltage condition causes the circuit it is protecting to be interrupted. As a prolonged undervoltage condition occurs on the power circuit controlled by breaker 10 and the voltage drops to sixty percent of normal voltage, the spring biasing means 43 and 44 of the undervoltage device 35 overcomes the magnetic attraction of the core 37 and coil 38 for armature 39. Thus, when the magnetic flux created by coil 38 of device 35 is low enough, the spring biasing means 43 and 44 actuates armature 39 away from core 37 causing trip hammer 47 of armature 39 to engage block 48. Block 48 is thereby rotated counterclockwise a portion of a revolution.

The counterclockwise rotation of block 48 rotates shaft 49 and block 108 engages roller 51 of one of the legs of star wheel 50 transmitting clockwise rotation to wheel 50. As the star wheel 50 rotates clockwise, roller 57 mounted on arm 55 of lever arm 53 (which in the contact closed position engages endwise one of the legs of star wheel 50) drops from endwise engagement therewith freeing rocker arm 53 for clockwise rotation about its pivot 56. The roller mounted on one end of the operating arm 62 exerts the forces of springs 77 and breaker contact springs 27 and 28 against outer surface 58 of rocker arm 53 and further causes a positive clockwise rotation of rocker arm 53. The roller on operating arm 62 becomes disengaged from outer surface 58, thus permitting pin 63 carried by one end of operating arm 62 to follow opening 60* in plate 59. The movement of the lower end of operating arm 62 (as shown in Fig. 1) permits operating arm 62 to pivot about the center point 70. Trip latch 64 has its latched cam surface 65 released from the trip pin 73, also freeing trip latch bar 74. The trip latch bar 74 rotates clockwise about its pivot 76. The pivoting of operating arm 62, aided by the spring 77 and breaker contact springs 27 and 28, causes the upper end of arm 62 (as shown in Fig. 1) to move counterclockwise to aid insulating arm 68, which being attached also to the contact arm 19, draws the contact arm 19 out of contact with the finger contact 18. Breaking the engagement of contact arm 19 and finger contact 18 transfers the current flow to arcing contacts 24, 25 which opens after finger contact 18 and contact arm 19 separate. The are drawn in the opening of arcing contacts 24, 25 travels upward toward an arc chute 102 defined by notched barrier plates 103. The are terminals leave arcing contacts 24, 25 and travel along an arc runner 26 and a contact extension 104, respectively. Arc chute 102, the barrier plates 103 and the effect of the magnetic iron core 105 arranged adjacent the underside of arc runner 26 in combination with the thermal and magnetic conditions caused by the arc aid in rapidly extinguishing the arc to interrupt the current in the power circuit controlled.

At the same time insulating arm 68 is drawn back to open breaker 10, the link 69 pivots clockwise about pivot 93 causing link 94 to pivot the open-closed breaker indicator 97 about shaft 95 indicating the open condition of the contacts of the breaker.

A clockwise rotation of handle 83 will manually restore the breaker to closed position, however, hydraulic means may be used, if so desired, in the manner shown and claimed in US. application Serial No. 560,497 of Julius W. Timmerman, filed January 23, 1956 and entitled Hydraulic Operating Means for a Circuit Breaker Structure.

In accordance with the invention claimed, the undervoltage trip device 35 is provided to trip the circuit breaker between thirty and sixty percent of the voltage rating of coil 38 and pick up, i.e., attract armature 39 to core 37, at eighty percent of its voltage rating. As disclosed in the drawings, spring biasing means such as the pair of coaxially arranged springs 43 and 44, shown in Fig. 1, or the conical spring means 106 shown in Fig. 3, are arranged to have a logarithmically shaped force-deflection curve which is so related to the logarithmically shaped characteristic solenoid pull curve that when the voltage drops to sixty percent of the rated voltage, the compressed spring biasing means will break open the air gap of the solenoid undervoltage trip device 35 and as the air gap widens the spring biasing means remains always below but very near the eighty percent voltage pull curve of the solenoid. The force available to trip the circuit breaker structure is the difierence between the force of the spring biasing means and the attraction force of the solenoid coil and core structure for its armature at whatever decreased voltage the solenoid coil has imposed upon it. With this arrangement, the force available to trip the circuit breaker is held to amaximum.

Fig. 4 illustrates the force vs. solenoid air gap characteristics for an undervoltage trip device as shown and claimed herein. Curves A, B and C illustrate solenoid pull curves for eighty, sixty, and thirty percent voltages, respectively, which are impressed upon the coil of the tripping device as shown. Curves D, E and H illustrate force-solenoid air gap characteristics for three different helical compression springs when used with the undervoltage trip device disclosed. Curves F and G illustrate, respectively, the force-solenoid air gap characteristics of a conical spring as shown in Fig. 3 and a pair of coaxially arranged helical spring biasing means 43 and 44 as shown in Fig. l of the undervoltage trip device 35. These spring means have a logarithmically shaped forcedeflection curve so related to the logarithmically shaped characteristic solenoid pull curve of device 35 that when the voltage impressed upon device 35 drops to sixty percent of rated voltage, the compressed spring biasing means will separate the armature of device 35 from its core 37 and as the air gap widens the spring force always remains below but very near the eighty percent voltage pull curve of the solenoid. As is readily noted from Fig. 4, the force-deflection characteristic for any single helical spring biasing means is not suificient to fulfill the requirements of the new and improved undervoltage trip device disclosed and claimed herein. It is evident from Fig. 4 that one spring biasing means is suflicient to provide the desired force-deflection characteristics if the spring is of a conical configuration.

Even though Fig. 1 illustrates the spring biasing means 43 and 44, operating through a crank arm at right angles to the center line of the solenoid armature, this is a preferred arrangement only and is not intended to limit the scope of the invention.

Although but two embodiments of the present inven tion have been illustrated and described, it will be appar ent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

What is claimed is:

1. An undervoltage trip device comprising a core structure, an armature disposed adjacent said structure to form therewith a magnetic circuit, a magnetizing winding for producing a magnetic flux in said magnetic circuit, and resilient means acting on said armature for opposing movement of said armature toward said structure, said resilient means having a logarithmically shaped force-deflection curve substantially similar to the logarithmically shaped characteristic pull curve of said magnetic circuit.

2. An undervoltage trip device comprising a core structure, an armature disposed adjacent said structure to form therewith a magnetic circuit, a magnetizing winding for producing a magnetic flux in said magnetic circuit, and spring biasing means acting on said armature for opposing movement of said armature toward said structure, said spring biasing means having a logarithmically shaped force-deflection curve substantially similar to the logarithmically shaped characteristic pull curve of said magnetic circuit.

3. An undervoltage trip device comprising a core structure, an armature disposed adjacent said structure to form therewith a magnetic circuit, a magnetizing winding for producing a magnetic flux in said magnetic circuit, and a conical shaped spring biasing means acting on said armature for opposing movement of said armature toward said structure, said spring biasing means having a logarithmically shaped force-deflection curve substantially similar to the logarthmically shaped characteristic pull curve of said magnetic circuit.

4. An undervoltage trip device comprising a core structure, an armature disposed adjacent said structure to form therewith a magnetic circuit, a magnetizing winding for producing a magnetic flux in said magnetic circuit, a pair of coaxially arranged springs acting on said armature for opposing movement of said armature toward said structure, said spring biasing means having a logarithmically shaped force-deflection curve substantially similar to the logarithmically shaped characteristic pull curve of said magnetic circuit.

5. An undervoltage trip device comprising a core structure, an armature disposed adjacent said structure to form therewith a magnetic circuit, a magnetizing winding for producing a magnetic flux in said magnetic circuit, and spring biasing means acting on said armature for opposing movement of said armature toward said structure, said biasing means having a logarithmically shaped force-deflection curve substantially similar to the logarithmically shaped characteristic pull curve of said magnetic circuit, so that when the voltage impressed upon said winding decreases to a predetermined value said biasing means actuates said armature relative to said structure to provide an air gap, the force of said biasing means remaining substantially constant as said air gap widens.

6. An undervoltage trip device comprising a core structure, an armature disposed adjacent said structure to form therewith a magnetic circuit, a magnetizing winding for producing a magnetic flux in said magnetic circuit, and spring biasing means acting on said armature for opposing movement of said armature toward said structure, said biasing means having a logarithmically shaped force-deflection curve substantially similar to the logarithmically shaped characteristic pull curve of said magnetic circuit so that when the voltage impressed upon said winding decreases to approximately sixty percent of rated voltage said biasing means actuates said armature relative to said structure to provide an air gap, the force of said biasing means remaining near the eighty percent value on said pull curve as said air gap widens.

7. An undervoltage trip device comprising a core 2,904,730 7 8 structure, an armature disposed adjacent said structure References Qited in the file, of this patent to form therewith a magnetic circuit, a magnetizing Wind- UNITED STATES PATENTS ing for producing a magnetic flux in said magnetic circuit, resilient means acting on said armature for opposing Em t movement of said armature toward said structure, said 5 4 41 Shuettmger 1949 resilient means having a logarithmically shaped forceaw n 2,565,989 Rady et al. Aug. 28, 1951 deflectlon curve substantially sunllar to the loganth- 2 636 935 h 1 A 28 1953 mically shaped characteristic pull curve of said mag- 1c ae netic circuit, and a time delay device connected to said armature for delaying the movement of said armature 10 away from said structure for a predetermined time. 

